Ultrasonic transducer driving circuit and ultrasonic image display apparatus

ABSTRACT

An ultrasonic transducer driving circuit configured to supply an output current and/or an output voltage to an output line for driving an ultrasonic transducer is provided. The ultrasonic transducer driving circuit includes a first current discharge circuit configured to allow a current arising from electric charges accumulated in the ultrasonic transducer to flow from the output line to ground when the output line is at a positive voltage, and a second current discharge circuit configured to allow the current arising from the electric charges accumulated in the ultrasonic transducer to flow from ground to the output line when the output line is at a negative voltage. The first current discharge circuit and the second current discharge circuit are controlled based on the output current and/or the output voltage.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/284,156 filed Oct. 28, 2011, which is hereby incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

The embodiments described herein relate to an ultrasonic transducerdriving circuit and ultrasonic image display apparatus.

An ultrasonic transducer driving circuit is a circuit that outputspulses comprised of positive pulses and negative pulses to an outputline toward an ultrasonic transducer and drives the ultrasonictransducer. As this kind of ultrasonic transducer driving circuit, avoltage output type circuit that controls an output voltage and suppliesan electrical current for driving an ultrasonic transducer is describedin, for example, Japanese Unexamined Patent Publication No. 2009-101072.In particular, the voltage output type circuit comprises a positivevoltage output circuit which outputs a positive voltage to theabove-mentioned output line and a negative voltage output circuit whichoutputs a negative voltage to the above-mentioned output line. In thisultrasonic transducer driving circuit, when negative pulses are to begenerated from a state in which the above-mentioned output line is at apositive voltage, the above-mentioned negative voltage output circuit istriggered to operate; and when positive pulses are to be generated froma state in which the above-mentioned output line is at a negativevoltage, the above-mentioned positive voltage output circuit istriggered to operate.

When the above-mentioned negative voltage output circuit is triggered tooperate when generating negative pulses from a state in which theabove-mentioned output line is supplied with a positive voltage, acurrent arising from electric charges which have been charged in theabove-mentioned ultrasonic transducer flows in this negative voltageoutput circuit for a certain period of time and power is consumed. Inturn, when the above-mentioned positive voltage output circuit istriggered to operate when generating positive pulses from a state inwhich the above-mentioned output line is at a negative voltage, acurrent arising from electric charges which have been charged in theabove-mentioned ultrasonic transducer flows in this positive voltageoutput circuit for a certain period of time and power is consumed.Therefore, reducing power consumption becomes a problem.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, an ultrasonic transducer driving circuit supplies anoutput current or an output voltage to an output line for driving anultrasonic transducer. The ultrasonic transducer driving circuitincludes a first current discharge circuit that, when the output line isat a positive voltage, allows a current arising from electric chargesaccumulated in the ultrasonic transducer to flow from the output line toground and a second current discharge circuit that, when the output lineis at a negative voltage, allows the current arising from electriccharges accumulated in the ultrasonic transducer to flow from ground tothe output line. The operations of the first and the second currentdischarge circuits are controlled in accordance with the output currentor the output voltage.

Here, the output current or the output voltage is a current or a voltageof an output line of the ultrasonic transducer driving circuit.

In another aspect, an ultrasonic transducer driving circuit includes acurrent output type circuit that controls an output current for drivingan ultrasonic transducer and a current control unit that outputs acurrent to the current output type circuit for controlling the outputcurrent. The current output type circuit includes a first currentdischarge circuit that, when the output line is at a positive voltage,allows a current arising from electric charges accumulated in theultrasonic transducer to flow from the output line to ground and asecond current discharge circuit that, when the output line is at anegative voltage, allows the current arising from electric chargesaccumulated in the ultrasonic transducer to flow from ground to theoutput line. The operations of the first current discharge circuit andthe second current discharge circuit are controlled by a current fromthe current control unit.

Here the output current is a current of an output line of the currentoutput type circuit.

In yet another aspect, an ultrasonic transducer driving circuit includesa voltage output type circuit that controls an output voltage andsupplies an electrical current to an output line for driving anultrasonic transducer and a first current discharge circuit and a secondcurrent discharge circuit connected to the output line. The firstcurrent discharge circuit is a circuit that, when the output line is ata positive voltage, allows a current arising from electric chargesaccumulated in the ultrasonic transducer to flow from the output line toground and the second current discharge circuit is a circuit that, whenthe output line is at a negative voltage, allows the current arisingfrom electric charges accumulated in the ultrasonic transducer to flowfrom ground to the output line. The operations of the first and secondcurrent discharge circuits are controlled by the voltage differencebetween the output line and the output of the voltage output typecircuit.

Here, the output voltage is a voltage of an output line of the voltageoutput type circuit.

In yet another aspect, an ultrasonic transducer driving circuit includesa voltage output type circuit that controls an output voltage andsupplies an electrical current to an output line for driving anultrasonic transducer and a buffer amplifier that is provided betweenthis voltage output type circuit and the ultrasonic transducer and takesinput of an output voltage of the voltage output type circuit. Thebuffer amplifier includes a first push-pull circuit having a firsttransistor and a second transistor connected to an output line of thebuffer amplifier and a second push-pull circuit having a thirdtransistor and a fourth transistor connected between the output line ofthe buffer amplifier and a ground. A voltage having a predeterminedvoltage difference relative to the output voltage of the voltage outputtype circuit is input to each of the transistors constituting the firstpush-pull circuit and the second push-pull circuit. The predeterminedvoltage difference is larger for the fourth transistor than for thesecond transistor, so that, when the output line of the buffer amplifieris at a positive voltage, the fourth transistor, of the secondtransistor and the fourth transistor, turns into an ON state inaccordance with an output voltage of the voltage output type circuit,thereby allowing the current arising from electric charges accumulatedin the ultrasonic transducer to flow from the output line to ground. Thepredetermined voltage difference is also larger for the third transistorthan for the first transistor, so that, when the output line of thebuffer amplifier is at a negative voltage, the third transistor, of thefirst transistor and the third transistor, turns into an ON state inaccordance with an output voltage of the voltage output type circuit,thereby allowing the current arising from electric charges accumulatedin the ultrasonic transducer to flow from ground to the output line.

Here, the output voltage is a voltage of an output line of the voltageoutput type circuit.

A further aspect includes an ultrasonic image display apparatus havingan ultrasonic transducer driving circuit pertaining to any of theaspects described above.

According to the aspects described above, when the output line is at apositive voltage, the current arising from electric charges accumulatedin the ultrasonic transducer flows from the output line to ground. Whenthe output line is at a negative voltage, the current arising fromelectric charges accumulated in the ultrasonic transducer flows fromground to the output line. Thereby, power consumption can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an exemplary embodiment of anultrasonic image display apparatus.

FIG. 2 is a block diagram showing a transceiving section of theultrasonic image display apparatus shown in FIG. 1.

FIG. 3 is a diagram showing an outlined structure of an ultrasonictransducer driving circuit in the ultrasonic image display apparatusshown in FIG. 1.

FIG. 4 is circuit diagram showing an ultrasonic transducer drivingcircuit in the ultrasonic image display apparatus shown in FIG. 1.

FIG. 5 is a diagram for explaining how a first current mirror circuitoperates.

FIG. 6 is a diagram for explaining how a fourth current mirror circuitoperates.

FIG. 7 is a diagram for explaining how a third current mirror circuitoperates.

FIG. 8 is a diagram for explaining how a second current mirror circuitoperates.

FIG. 9 is a circuit diagram showing an ultrasonic transducer drivingcircuit of a second embodiment.

FIG. 10 is a diagram showing a voltage waveform with five levels ofvoltages.

FIG. 11 is a circuit diagram showing another example of an ultrasonictransducer driving circuit of the second embodiment.

FIG. 12 is a diagram showing one example of a waveform of an outputvoltage that is output from a voltage output type circuit.

FIG. 13 is a diagram for explaining how the ultrasonic transducerdriving circuit of the second embodiment operates.

FIG. 14 is a diagram for explaining how the ultrasonic transducerdriving circuit of the second embodiment operates.

FIG. 15 is a diagram for explaining how the ultrasonic transducerdriving circuit of the second embodiment operates.

FIG. 16 is a diagram for explaining how the ultrasonic transducerdriving circuit of the second embodiment operates.

FIG. 17 is a circuit diagram showing an ultrasonic transducer drivingcircuit of a first example of modification to the second embodiment.

FIG. 18 is a circuit diagram in which switches were turned off in theultrasonic transducer driving circuit shown in FIG. 17.

FIG. 19 is a circuit diagram showing an ultrasonic transducer drivingcircuit of a second example of modification to the second embodiment.

FIG. 20 is a circuit diagram showing an ultrasonic transducer drivingcircuit of a third embodiment.

FIG. 21 is a diagram for explaining how the ultrasonic transducerdriving circuit of the third embodiment operates.

FIG. 22 is a diagram for explaining how the ultrasonic transducerdriving circuit of the third embodiment operates.

FIG. 23 is a diagram for explaining how the ultrasonic transducerdriving circuit of the third embodiment operates.

FIG. 24 is a diagram for explaining how the ultrasonic transducerdriving circuit of the third embodiment operates.

DETAILED DESCRIPTION OF THE INVENTION

In the following, embodiments of the present invention will be describedin detail based on the drawings.

First Embodiment

To begin with, a first embodiment is described based on FIGS. 1-8. Asshown in FIG. 1, an ultrasonic image display apparatus 100 includes anultrasonic probe 101, a transceiver unit 102, an echo data processingunit 103, a display control unit 104, a display unit 105, an operationalunit 106, and a control unit 107.

The ultrasonic probe 101 is provided with a plurality of ultrasonictransducers 101 a for transmitting and receiving ultrasonic waves.

The transceiver unit 102 includes a transmitter unit 1021 and a receiverunit 1022, as shown in FIG. 2. The transmitter unit 1021 supplies anelectric signal for transmitting ultrasonic waves under predeterminedscanning conditions to the ultrasonic transducers 101 a, based on acontrol signal from the control unit 107. The transmitter unit 1021includes ultrasonic transducer driving circuits 1 that supply anelectric signal for driving the ultrasonic transducers 101 a and causingthem to transmit ultrasonic waves (not shown in FIG. 2; see FIG. 3).Further description about the ultrasonic transducer driving circuits 1will be provided later.

The receiver unit 1022 performs signal processing such as A/Dconversion, phasing and addition, etc. on an echo signal received by theultrasonic probe 2 and outputs resulting echo data to the echo dataprocessing unit 103.

The echo data processing unit 103 performs processing for producing anultrasonic image on echo data which has been input from the transceiverunit 102. For example, the echo data processing unit 103 performs B-modeprocessing such as logarithmic compression and envelope detection andDoppler processing such as quadrature detection and filtering.

The display control unit 104 performs scan conversion of data obtainedby the echo data processing unit 103 using a scan converter and producesultrasonic image data. Then, the display control unit 104 causes thedisplay unit 105 to display an ultrasonic image in accordance with theultrasonic image data.

The display unit 105 includes an LCD (liquid crystal display), a CRT(Cathode Ray tube), or any other type of display. The operational unit106 includes a keyboard and a pointing device (not shown) or the likefor allowing an operator to enter a command and information.

The control unit 107 includes a CPU (Central Processing Unit). Thiscontrol unit 107 reads a control program stored in a memory unit whichis not shown and causes respective components of the ultrasonic imagedisplay apparatus 100 to perform their functions.

Description about the ultrasonic transducer driving circuits 1 isprovided based on FIGS. 3 and 4. The number of the (plural) ultrasonictransducer driving circuits 1 corresponds to a maximum number of theultrasonic transducers 101 a which are used for transmission (only oneof them is shown in FIG. 3). Each of the ultrasonic transducer drivingcircuits 1 includes a current DAC (Digital to Analog Converter) 2 and acurrent output type circuit 3. The current output type circuit 3controls an output current flowing through an output line O and supplieselectrical currents to the output line O for driving the correspondingultrasonic transducer 101 a. This output line O is one example of anembodiment of an output line.

In fact, the output line O is the output line of the current output typecircuit 3 and also the output line of each of the ultrasonic transducerdriving circuits 1. The output line of the current output type circuit 3is the output line of each of the ultrasonic transducer driving circuits1.

The current DAC 2 includes a positive current DAC 21 and a negativecurrent DAC 22. The current output type circuit 3 includes a positivecurrent output type circuit 31 and a negative current output typecircuit 32. The current DAC 2 is one example of an embodiment of acurrent control. The current output type circuit 3 is one example of anembodiment of a current output type circuit.

The positive current DAC 21 and the negative current DAC 22 output acurrent for controlling an output current of the positive current outputtype circuit 31 and the negative current output type circuit 32.

The positive current DAC 21 is connected to the positive current outputtype circuit 31. The output current of the positive current output typecircuit 31 is controlled by the current that is output from the positivecurrent DAC 21 to the positive current output type circuit 31. Thenegative current DAC 22 is connected to the negative current output typecircuit 32. The output current of the negative current output typecircuit 32 is controlled by the current that is output from the negativecurrent DAC 22 to the negative current output type circuit 32.

By the way, in conjunction with controlling the output currents of thepositive current output type circuit 31 and the negative current outputtype circuit 32, the operations of a second current mirror circuit 312and a fourth current mirror circuit 322 which will be described laterare controlled. More specifically, the operations of the second currentmirror circuit 312 and the fourth current mirror circuit 322 arecontrolled by the currents that are output from the positive current DAC21 and the negative current DAC 22.

The positive current output type circuit 31 outputs a positive currentto the corresponding ultrasonic transducer 101 a. On the other hand, thenegative current output type circuit 32 outputs a negative current tothe corresponding ultrasonic transducer 101 a.

How the positive current output type circuit 31 and the negative currentoutput type circuit 32 are configured is described in detail based onFIG. 4. The positive current output type circuit 31 includes a firstcurrent mirror circuit 311, a second current mirror circuit 312, and apositive current switching circuit 313. The first current mirror circuit311 is configured with a transistor Tr1 and a transistor Tr2. The secondcurrent mirror circuit 312 is configured with a transistor Tr3 and atransistor Tr4. The positive current switching circuit 313 is configuredwith a transistor Tr5 and a transistor Tr6. The transistors Tr1 to Tr4are p-channel type MOSFETs (Metal-Oxide Semiconductor Field-EffectTransistors). The transistors Tr5, Tr6 are n-channel type MOSFETs.

The operations of the first current mirror circuit 311 and the secondcurrent mirror circuit 312 are controlled by the output current of thepositive current DAC 21, as will be described later. The first currentmirror circuit 311 is one example of an embodiment of a positive currentmirror circuit. The second current mirror circuit 312 is one example ofan embodiment of a second current discharge circuit.

For the transistors Tr1, Tr2, their gate terminals are connected to eachother and their source terminals are connected to a power supply voltage+HV. A drain terminal of the transistor Tr1 is connected to a drainterminal of the transistor Tr6 and a drain terminal of the transistorTr2 is connected to the output line O.

For the transistors Tr3, Tr4, their gate terminals are connected to eachother and their source terminals are connected to a ground. A drainterminal of the transistor Tr3 is connected to the transistor Tr5 and adrain terminal of the transistor Tr4 is connected to the output line O.Besides, a diode D1 is connected between a drain terminal of thetransistor Tr4 and the output line O. This diode D1 is connected,oriented so that a current flows from the transistor Tr4 toward theoutput line O.

For the transistors Tr5, Tr6, their source terminals are connected tothe positive current DAC 21. A gate terminal of the transistor Tr5 isconnected to a voltage −VrefGND and a gate terminal of the transistorTr6 is connected to the output line O. By the way, −VrefGND is a voltagethat is lower by a predetermined voltage than ground.

The positive current switching circuit 313 formed of the transistorsTr5, Tr6 is a differential amplifier circuit in which the transistor Tr6will be OFF when the transistor Tr5 is put in an ON state, whereas thetransistor Tr6 will be ON when the transistor Tr5 is put in an OFFstate. The transistor Tr6 is put in an ON state when the output line Ois at a positive voltage and in an OFF state when the output line O isat a negative voltage. Hence, the transistor Tr5 is put in an OFF statewhen the output line O is at a positive voltage and in an ON state whenthe output line O is at a negative voltage.

The negative current output circuit 32 includes a third current mirrorcircuit 321, a fourth current mirror circuit 322, and a negative currentswitching circuit 323. The third current mirror circuit 321 isconfigured with a transistor Tr7 and a transistor Tr8. The fourthcurrent mirror circuit 322 is configured with a transistor Tr9 and atransistor Tr10. The negative current switching circuit 323 isconfigured with a transistor Tr11 and a transistor Tr12. The transistorsTr7 to Tr10 are n-channel type MOSFETs (Metal-Oxide SemiconductorField-Effect Transistors). The transistors Tr11, Tr12 are p-channel typeMOSFETs.

The third current mirror circuit 321 is one example of an embodiment ofa negative current mirror circuit. The fourth current mirror circuit 322is one example of an embodiment of a first current discharge circuit.

For the transistors Tr7, Tr8, their gate terminals are connected to eachother and their source terminals are connected to a power supply voltage−HV. A drain terminal of the transistor Tr7 is connected to a drainterminal of the transistor Tr12 and a drain terminal of the transistorTr8 is connected to the output line O.

For the transistors Tr9, Tr10, their gate terminals are connected toeach other and their source terminals are connected to a ground. A drainterminal of the transistor Tr9 is connected to the transistor Tr11 and adrain terminal of the transistor Tr10 is connected to the output line O.Besides, a diode D2 is connected between the drain terminal of thetransistor Tr10 and the output line O. This diode D2 is connected to beoriented so that a current flows from the output line O toward thetransistor Tr10.

For the transistors Tr11, Tr12, their source terminals are connected tothe negative current DAC 22. A gate terminal of the transistor Tr11 isconnected to a voltage +VrefGND and a gate terminal of the transistorTr12 is connected to the output line O. By the way, +VrefGND is avoltage that is higher by a predetermined voltage than ground.

The negative current switching circuit 323 formed of the transistorsTr11, Tr12 is a differential amplifier circuit in which the transistorTr12 will be OFF when the transistor Tr11 is put in an ON state, whereasthe transistor Tr12 will be ON when the transistor Tr11 is put in an OFFstate. The transistor Tr12 is put in an OFF state when the output line Ois at a positive voltage and in an ON state when the output line O is ata negative voltage. Hence, the transistor Tr11 is put in an ON statewhen the output line O is at a positive voltage and in an OFF state whenthe output line O is at a negative voltage.

Then, how an ultrasonic transducer driving circuit 1 of the presentexample operates is described. In this ultrasonic transducer drivingcircuit 1, a positive current is output from the positive current outputtype circuit 31 and a negative current is output from the negativecurrent output type circuit 32 and electrical currents for driving thecorresponding ultrasonic transducer 101 a are output. This is explainedspecifically below.

First, the first current mirror circuit 311 operates and a positivecurrent +Io is output. Concretely speaking, as shown in FIG. 5, anegative current −Ii is input from the positive current DAC 21 to thepositive current output type circuit 31. At this time, the transistorTr6 is put in an ON state and there is a current I6 flowing through thistransistor Tr6. This, in consequence, produces a current I1 flowingthrough the transistor Tr1 and a current I2 flowing through thetransistor Tr2. This current I2 is output to the output line O as thepositive current +Io and the voltage of this output line O rises andbecomes a positive voltage.

Then, the fourth current mirror circuit 322 operates and the output ofthe positive current +Io causes discharging of electric chargesaccumulated in the ultrasonic transducer 101 a. Concretely, as shown inFIG. 6, instead of the input of the negative current −Ii from thepositive current DAC 21 to the positive current output type circuit 31,a positive current +Ii is input from the negative current DAC 22 to thenegative current output type circuit 32. At this time, the transistorTr11 is put in an ON state and, therefore, the positive current +Iiproduces a current I11 flowing through the transistor Tr11, a current I9flowing through the transistor Tr9, and a current I10 flowing throughthe transistor Tr10. This current I10 is a current arising from electriccharges accumulated in the ultrasonic transducer 101 a and is oneexample of an embodiment of a current flowing from the output line toground.

In turn, the third current mirror circuit 321 operates. Concretely, theflowing of the current I10 causes a decrease in the voltage (positivevoltage) of the output line O. Then, when the voltage of the output lineO comes to the voltage +VrefGND, the transistor Tr12 turns into an ONstate, whereas the transistor Tr11 turns into an OFF state. As shown inFIG. 7, the turning of the transistor Tr12 into the ON state produces acurrent I12 flowing through this transistor Tr12. This, in consequence,produces a current I7 flowing through the transistor Tr7 and a currentI8 flowing through the transistor Tr8. This current I8 is output to theoutput line O as a negative current −Io and the voltage of this outputline O falls and becomes a negative voltage.

Then, the second current mirror circuit 312 operates and the output ofthe negative current −Io causes discharging of electric chargesaccumulated in the ultrasonic transducer 101 a. Concretely, as shown inFIG. 8, instead of the input of the positive current +Ii from thenegative current DAC 22 to the negative current output type circuit 32,the negative current −Ii is input from the positive current DAC 21 tothe positive current output type circuit 31. At this time, thetransistor Tr5 is put in an ON state and, therefore, the negativecurrent −Ii produces a current I5 flowing through the transistor Tr5, acurrent I3 flowing through the transistor Tr3, and a current I4 flowingthrough the transistor Tr4. This current I4 is a current arising fromelectric charges accumulated in the ultrasonic transducer 101 a and isone example of an embodiment of a current flowing from ground to theoutput line.

The flowing of the current I4 causes an increase of the voltage(negative voltage) of the output line O. Then, when the voltage of theoutput line O comes to the voltage −VrefGND, the transistor Tr6 turnsinto an ON state, whereas the transistor Tr5 turns into an OFF state.The turning of the transistor Tr6 into the ON state produces the currentI2 again and the positive current +Io is supplied to the output line O.

According to the ultrasonic transducer driving circuit 1 of the presentexample, when the output line O is at a positive voltage, the currentarising from electric charges accumulated in the ultrasonic transducer101 a flows from the output line O to ground via the fourth currentmirror circuit 322. Likewise, when the output line O is at a negativevoltage, the current arising from electric charges accumulated in theultrasonic transducer 101 a flows from ground to the output line O viathe second current mirror circuit 312. In this way, the current arisingfrom electric charges accumulated in the ultrasonic transducer 101 adoes not flow through the first current mirror circuit 311 and the thirdcurrent mirror circuit 321 and, thus, power consumption can be reduced.

Second Embodiment

Next, a second embodiment is described. Ultrasonic transducer drivingcircuits 50 of the present example are provided in the transmitter unit1021 of the ultrasonic image display apparatus 100 (see FIG. 1 and FIG.2), as is the case for the ultrasonic transducer driving circuits 1 ofthe first embodiment.

As shown in FIG. 8, each of the ultrasonic transducer driving circuits50 includes a voltage output type circuit 51, a first current dischargecircuit 52, and a second current discharge circuit 53. The voltageoutput type circuit 51 controls an output voltage of an output line Oand supplies an electrical current to an output line O for driving thecorresponding ultrasonic transducer 101 a. This output line O is oneexample of an embodiment of an output line.

The output line O is the output line of the voltage output type circuit51 and also the output line of each of the ultrasonic transducer drivingcircuits 1. The output line of the voltage output type circuit 51 is theoutput line of each of the ultrasonic transducer driving circuits 50.

The voltage output type circuit 51 is a multi-level pulser having threeor more levels of output voltages. For example, the voltage output typecircuit 51 outputs five levels of voltages as output voltages, as isillustrated in FIG. 10. This is, however, not to be regarded aslimiting.

The voltage output type circuit 51 includes an operational amplifier511. To this operational amplifier 511, a positive power supply 512which supplies a positive supply voltage and a negative power supply 513which supplies a negative supply voltage are connected.

Besides, a power supply 514 is connected to a non-inverting inputterminal (+) of the operational amplifier 511. On end of this powersupply 514 is connected to the non-inverting input terminal (+) and theother end is connected to a ground.

A resistor R1 is connected between an inverting input terminal (−) ofthe operational amplifier 511 and the ground. The other end of afeedback line FL whose one end is connected to the output line O andhaving a resistor R2 is connected between this resistor R1 and theinverting input terminal (−). Thus, by way of this feedback line FL, theoutput voltage of the output line O is divided by the resistor R2 andinput to the inverting input terminal (−).

The first current discharge circuit 52 and the second current dischargecircuit 53 are provided along the output line O. In other words, thefirst current discharge circuit 52 and the second current dischargecircuit 53 are provided between the voltage output type circuit 51 andthe corresponding ultrasonic transducer 101 a. The first currentdischarge circuit 52 is configured with a current mirror circuit havingtransistors Tr21 and Tr22. The second current discharge circuit 53 isconfigured with a current mirror circuit having transistors Tr23 andTr24. The transistors Tr21 and Tr22 are p-channel type MOSFETs and thetransistors Tr23 and Tr24 are n-channel type MOSFETs.

For the transistors Tr21 and Tr22, their gate terminals are connected toeach other and their source terminals are connected to the ultrasonictransducer 101 a. A drain terminal of the transistor Tr21 is connectedto the voltage output type circuit 51 and a drain terminal of thetransistor Tr22 is connected to the ground.

For the transistors Tr23, Tr24, their gate terminals are connected toeach other and their source terminals are connected to the ultrasonictransducer 101 a. A drain terminal of the transistor Tr23 is connectedto the voltage output type circuit 51 and a drain terminal of thetransistor Tr24 is connected to the ground.

Here, a path between the transistors T21, T22 and an output terminal ofthe operational amplifier 511 is assumed as a first output line O1. Apath between the transistors Tr21 to Tr24 and the ultrasonic transducer101 a is assumed as a second output line O2. That is, the output lineincludes the first output line O1 and the second output line O2. One endof the first output line O1 is connected to the output terminal of theoperational amplifier 511 and the other end branches to connect to thedrain terminals of the transistors Tr21 and Tr23.

The operations of the first current discharge circuit 52 and the secondcurrent discharge circuit 53 are controlled according to an outputvoltage of the voltage output type circuit 51. In the present example,the operations of the first current discharge circuit 52 and the secondcurrent discharge circuit 53 are controlled by the voltage differencebetween the second output line O2 and the first output line O1. Furtherdetails will be provided later.

Diodes D21 and D23 are connected at points on the branches of the firstoutput line O1. The diode D21 is connected to be oriented so that acurrent flows from the transistor Tr21 toward the output terminal of theoperational amplifier 511. The diode D23 is connected to be oriented sothat a current flows from the output terminal of the operationalamplifier 511 toward the transistor Tr23.

However, the diodes D21 and D23 may not necessarily be provided.

A diode D22 is connected between the transistor Tr22 and the ground. Adiode D24 is connected between the transistor Tr24 and the ground. Thediode D22 is connected to be oriented so that a current flows from thetransistor Tr22 toward the ground. The diode D24 is connected to beoriented so that a current flows from the ground toward the transistorTr24.

Here, as shown in FIG. 11, the diode D21 may be connected between thesource terminal of the transistor Tr21 and the second output line O2.The diode D22 may be connected between the source terminal of thetransistor Tr22 and the second output line O2. The diode D23 may beconnected between the transistor Tr23 and the second output line O2. Thediode D24 may be connected between the transistor Tr24 and the secondoutput line O2.

Although not shown particularly, an additional circuit may be providedto avoid an excessive inverse voltage between the gate and sourceterminals of the transistors Tr21 to Tr24.

Then, how an ultrasonic transducer driving circuit 1 of the presentexample operates is described. In this ultrasonic transducer drivingcircuit 1, a voltage having a waveform that is shown in FIG. 12 isoutput from the voltage output type circuit 51. In FIG. 12, the waveformof an output voltage is simplified and represented as a sine wave.

In a state in which the second output line O2 is at a ground voltage,when an output voltage starts to be supplied from the voltage outputtype circuit 51 to the first output line O1 at time t1, the voltage ofthis first output line O1 rises and the output voltage becomes apositive voltage. This produces a current I23 flowing through thetransistor Tr23, as shown in FIG. 13, and the voltage of the secondoutput line O2 rises.

Then, after the output voltage of the voltage output type circuit 51 hasreached a peak at time t2, when it starts to fall, the voltage of thesecond output line O2 becomes smaller than that of the first output lineO1, thereby producing a current I21 flowing through the transistor Tr21and a current I22 flowing through the transistor Tr22, as shown in FIG.14. The current I21 is a current that flows from the second output lineO2 toward the first output line O1. The current I22 is a current thatflows from the second output line O2 toward the ground.

Then, after the output voltage of the voltage output type circuit 51 hasbecome equal to the ground voltage at time t3, when it further falls andbecomes a negative voltage, the second output line O2 becomes lower thanthe ground voltage, thus resulting in that the current I21 only flows,but the current I22 does not flow, as shown FIG. 15.

Then, after the output voltage of the voltage output type circuit 51 hasbecome minimum, when it starts to rise, the voltage of the first outputline O1 becomes larger than that of the second output line O2, therebyproducing a current I23 flowing through the transistor Tr23 and acurrent I24 flowing through the transistor Tr24, as shown in FIG. 16.The current I23 is a current that flows from the first output line O1toward the second output line O2. The current I23 is a current thatflows from the ground toward the second output line O2.

According to the ultrasonic transducer driving circuits 50 of thepresent example, when the output line O is at a positive voltage, thecurrent arising from electric charges accumulated in the ultrasonictransducer 101 a flows from the second output line O2 to the ground asthe current I22 via the first current discharge circuit 52 and alsoflows from the second output line O2 to the first output line O1 as thecurrent I21. Therefore, power consumption can be reduced by an amountequivalent to the amount of the current I22 flowing.

Likewise, when the output line O is at a negative voltage, the currentarising from electric charges accumulated in the ultrasonic transducer101 a flows from the ground to the second output line O2 as the currentI24 via the second current discharge circuit 53 and also flows from thefirst output line O1 to the second output line O2 as the current I23.Therefore, power consumption can be reduced by an amount equivalent tothe amount of the current I24 flowing.

Next, examples of modification to the second embodiment are described.To being with, a first modification example is described. In anultrasonic transducer driving circuit 50 of the first modificationexample, a switch SW1 is provided on a connection path between thetransistors Tr21 and Tr22, that is, between the gate terminals of thetransistors Tr21 and Tr22, as shown in FIG. 17. Besides, a switch SW2 isprovided on a connection path between the transistors Tr23 and Tr24,that is, between the gate terminals of the transistors Tr23 and Tr24. Asshown in FIG. 18, by turning the switches SW1 and SW2 off, it ispossible to make the transistors Tr22 and Tr24 and the diodes D22 andD24 operate as a ground clamp circuit that keeps the voltage of theoutput line O at the ground voltage level.

Then, a second modification example is described. In an ultrasonictransducer driving circuit 50 of the second modification example,instead of the voltage output type circuit 51, a voltage output typecircuit 51′ shown in FIG. 19 is connected to the output line O. Theultrasonic transducer driving circuit 50 of the second modificationexample outputs two levels of voltages as output voltages.

The voltage output type circuit 51′ includes a positive voltage outputcircuit 54 and a negative voltage output circuit 55. Both the positivevoltage output circuit 54 and the negative voltage output circuit 55output a voltage to the output line O. The positive voltage outputcircuit 54 outputs a positive voltage to the output line O and thenegative voltage output circuit 55 outputs a negative voltage to theoutput line O.

The positive voltage output circuit 54 includes a positive supplyvoltage +HV, a transistor Tr25, and a diode D25. The diode D25 isconnected between the transistor Tr25 and the output line O.

The transistor Tr25 is a p-channel type MOSFET in which the positivesupply voltage +HV is connected to its source terminal and the diode D2is connected to its drain terminal To a gate terminal of the transistorTr25, a first driver circuit 56 is connected that outputs a drive signalto turn the transistor Tr25 on/off.

The negative voltage output circuit 55 includes a negative supplyvoltage −HV, a transistor Tr26, and a diode D26. The diode D26 isconnected between the transistor Tr26 and the output line O.

The negative voltage output circuit 55 is an n-channel MOSFET in whichthe negative supply voltage −HV is connected to its source terminal andthe diode D26 is connected to its drain terminal To a gate terminal ofthe transistor Tr26, a second driver circuit 57 is connected thatoutputs a drive signal to turn the transistor Tr26 on/off.

How the circuit of the second modification example operates isdescribed. At time t1, as shown in FIG. 12, the transistor Tr25 turnsinto an ON state. This produces a current I23 flowing through thetransistor Tr23 and the voltage of the output line O rises.

Then, at time t2, the transistor Tr25 turns into an OFF state and thetransistor Tr26 turns into an ON state. This causes a decrease in thevoltage of the first output line O1, thereby producing currents I21 andI22 flowing through the transistors Tr21 and Tr22.

Then, at time t4, the transistor Tr26 turns into an OFF state and thetransistor Tr25 turns into an ON state. This causes an increase in thevoltage of the first output line O1, thereby producing currents I23, I24flowing through the transistors Tr23, Tr24.

Third Embodiment

Next, a third embodiment is described. Ultrasonic transducer drivingcircuits 70 of the present example are provided in the transmitter unit1021 of the ultrasonic image display apparatus 100 (see FIG. 1 and FIG.2), as is the case for the ultrasonic transducer driving circuits 1 ofthe first embodiment and the ultrasonic transducer driving circuits 50of the second embodiment.

As shown in FIG. 20, each of the ultrasonic transducer driving circuits70 includes a voltage output type circuit 71 and a buffer amplifier 72.The voltage output type circuit 71 controls an output voltage of anoutput line O and supplies an electrical current to an output line O fordriving the corresponding ultrasonic transducer 101 a. This output lineO corresponds to an output line of the voltage output type circuit 71.The output line O includes an output line of the ultrasonic transducerdriving circuit 70. The output line O is one example of an embodiment ofan output line.

Here, a detailed configuration of the voltage output type circuit 71 isnot shown.

The buffer amplifier 72 is provided along the output line O of thevoltage output type circuit 71. Here, the output line includes an inputline IL to the buffer amplifier 72 and an output line Ob of the bufferamplifier 72. To the buffer amplifier 72, an output voltage of thevoltage output type circuit 71 is input through the input line IL.

The output line Ob of the buffer amplifier 72 is also the output line ofthe ultrasonic transducer driving circuit 70.

The buffer amplifier 72 includes a first push-pull circuit 73 and asecond push-pull circuit 74. The first push-pull circuit 73 isconfigured with transistors Tr31 and Tr32. The second push-pull circuit74 is configured with transistors Tr33 and Tr34. The transistors Tr31and Tr33 are npn type bipolar transistors. The transistors Tr32 and Tr34are pnp type bipolar transistors.

The first push-pull circuit 73 is one example of an embodiment of afirst push-pull circuit and the second push-pull circuit 74 is oneexample of an embodiment of a second push-pull circuit. Besides, thetransistor Tr31 is one example of an embodiment of a first transistorand the transistor Tr32 is one example of an embodiment of a secondtransistor. Further, the transistor Tr33 is one example of an embodimentof a third transistor and the transistor Tr34 is one example of anembodiment of a fourth transistor.

In the first push-pull circuit 73, emitter terminals of the transistorsTr31 and Tr32 are connected to each other. In the second push-pullcircuit 74, emitter terminals of the transistors Tr33 and Tr34 areconnected to each other. The output line Ob of the buffer amplifier 72is connected between the transistors Tr31 and Tr32, and between thetransistors Tr33 and Tr34.

A positive supply voltage +HV is connected to a collector terminal ofthe transistor Tr31. A negative supply voltage −HV is connected to acollector terminal of the transistor Tr32.

Collector terminals of the transistors Tr33 and Tr34 are connected to aground.

Between the positive supply voltage +HV and the input line IL, a currentsource IS1 and a schottky diode D31 are provided. The current source IS1is arranged to the positive supply voltage +HV and the schottky diodeD31 is arranged to the input line IL. A base terminal of the transistorTr31 is connected between the current source IS1 and the schottky diodeD31.

Between the negative supply voltage −HV and the input line IL, a currentsource IS2 and a schottky diode D32 are provided. The current source IS2is arranged to the negative supply voltage −HV and the schottky diodeD32 is arranged to the input line IL. A base terminal of the transistorTr32 is connected between the current source IS2 and the schottky diodeD32.

Between the positive supply voltage +HV and the input line IL, a currentsource IS3 and a diode 33 are also provided in parallel with the currentsource IS1 and the schottky diode D31. The current source IS3 isarranged to the positive supply voltage +HV and the diode D33 isarranged to the input line IL. A base terminal of the transistor Tr33 isconnected between the current source IS3 and the diode D33.

Likewise, between the negative supply voltage −HV and the input line IL,a current source IS4 and a diode 34 are provided in parallel with thecurrent source IS2 and the schottky diode D32. The current source IS3 isarranged to the negative supply voltage −HV and the diode D34 isarranged to the input line IL. A base terminal of the transistor Tr34 isconnected between the current source IS4 and the diode D34.

To the transistors Tr31 to Tr34, a voltage having a predetermineddifference relative to the voltage of the input line IL, that is, theoutput voltage of the voltage output type circuit 71 is input. Forexample, the potential of the base terminal of the transistor Tr31 is0.3 V higher than the potential of the input line IL and the potentialof the base terminal of the transistor Tr33 is 0.7 V higher than thepotential of the input line IL. The potential of the base terminal ofthe transistor Tr32 is 0.3 V lower than the potential of the input lineIL and the potential of the base terminal of the transistor Tr34 is 0.7V lower than the potential of the input line IL.

The potential difference between the base terminal of the transistorTr33 and the input line IL is larger than the potential differencebetween the base terminal of the transistor Tr31 and the input line IL.The potential difference between the base terminal of the transistorTr34 and the input line IL is larger than the potential differencebetween the base terminal of the transistor Tr32 and the input line IL.

Due to the fact that the potential differences of the base terminals ofthe transistors Tr31, Tr33 and the input line IL are as above, when theoutput line Ob is at a negative voltage, the transistor Tr33, of thetransistor Tr31 and the transistor Tr33, turns into an ON state inaccordance with an output voltage of the voltage output type circuit 71,thereby allowing the current arising from electric charges accumulatedin the ultrasonic transducer 101 a to flow from ground to the outputline Ob. Further details will be provided later.

Due to the fact that the potential differences of the base terminals ofthe transistors Tr32, Tr34 and the input line IL are as above, when theoutput line Ob is at a positive voltage, the transistor Tr34, of thetransistor Tr32 and the transistor Tr34, turns into an ON state inaccordance with an output voltage of the voltage output type circuit 71,thereby allowing the current arising from electric charges accumulatedin the ultrasonic transducer 101 a to flow from the output line Ob toground. Further details will be provided later.

Then, how the ultrasonic transducer driving circuit 70 operates isdescribed. A voltage having a waveform that is shown in FIG. 12, as isthe case for the second embodiment, is output from the voltage outputtype circuit 71. In a state in which the output line Ob is at a groundvoltage, when an output voltage starts to be supplied from the voltageoutput type circuit 71 to the input line IL at time t1, the voltage ofthis input line IL rises. With the rise of the voltage of this inputline IL, a base-emitter voltage of the transistor Tr31 rises and thetransistor Tr31 turns into an ON state. This produces a current I31flowing through the transistor Tr31, as shown in FIG. 21, and thevoltage of the output line Ob rises.

Then, after the output voltage of the voltage output type circuit 71 hasreached a peak at time t2, when it starts to fall, the transistor Tr31turns into an OFF state due to a decrease in its base voltage. As theoutput voltage of the voltage output type circuit 71 falls, the basevoltages of the transistors 32 and 34 fall. Because the turning of thetransistor Tr31 into the OFF state stops the rise of the voltage of theoutput line Ob, the falling base voltages of the transistors Tr32 andTr34 cause an increase in the potential difference of base terminal withrespect to emitter terminal in the transistors Tr32 and Tr34.

Here, as mentioned above, the potential difference between the baseterminal of the transistor Tr34 and the input line IL is larger than thepotential difference between the base terminal of the transistor Tr32and the input line IL. Therefore, the transistor Tr34 turns into an ONstate earlier than the transistor Tr32, thereby producing a current I34flowing through the transistor Tr34, as shown in FIG. 22.

After the transistor Tr34 has turned into the ON state, until the outputvoltage of the voltage output type circuit 71 comes to the groundvoltage at time t3, the voltage of the input line IL and the voltage ofthe output line Ob fall in a state in which the voltage of the baseterminal with respect to the emitter terminal of the transistor Tr34 isequal to the voltage of the base terminal of the transistor Tr34 withrespect to the input line IL. After the output voltage of the voltageoutput type circuit 71 has come to the ground voltage at time t3, whenit further falls, the voltage of the base terminal with respect to theemitter terminal of the transistor Tr32 falls and the transistor Tr32turns into an ON state, as the voltage of the output line Ob remains atthe ground voltage. This, in consequence, produces a current I32 flowingthrough the transistor Tr32, as shown in FIG. 23, and the voltage of theoutput line Ob falls.

Then, after the output voltage of the voltage output type circuit 71 hasbecome minimum, when it starts to rise, the transistor Tr32 turns intoan OFF state due to a rise of its base voltage. As the output voltage ofthe voltage output type circuit 71 rises, the base voltages of thetransistors Tr31 and Tr33 rise. Because the turning of the transistorTr32 into the OFF state stops the fall of the voltage of the output lineOb, the rising base voltages of the transistors Tr31 and Tr33 cause anincrease in the potential difference of base terminal with respect toemitter terminal in the transistors Tr31 and Tr33.

Here, as mentioned above, the potential difference between the baseterminal of the transistor Tr33 and the input line IL is larger than thepotential difference between the base terminal of the transistor Tr31and the input line IL. Therefore, the transistor Tr33 turns into an ONstate earlier than the transistor Tr31, thereby producing a current I33flowing through the transistor Tr33, as shown in FIG. 24.

After the transistor Tr33 has turned into the ON state, until the outputvoltage of the voltage output type circuit 71 comes to the groundvoltage at time t4, the voltage of the input line IL and the voltage ofthe output line Ob rise in a state in which the voltage of the baseterminal with respect to the emitter terminal of the transistor Tr33 isequal to the voltage of the base terminal of the transistor Tr33 withrespect to the input line IL. After the output voltage of the voltageoutput type circuit 71 has come to the ground voltage at time t4, whenit further rises, the voltage of the base terminal with respect to theemitter terminal of the transistor Tr31 rises and the transistor Tr31turns into an ON state again, as the voltage of the output line Obremains at the ground voltage.

According to the ultrasonic transducer driving circuit 50 of the presentexample, when the output line Ob is at a positive voltage, the currentarising from electric charges accumulated in the ultrasonic transducer101 a flows from the output line Ob to ground as the current I34, due tothe fact that the transistor Tr34 turns into an ON state. When theoutput line Ob is at a negative voltage, the current arising fromelectric charges accumulated in the ultrasonic transducer 101 a flowsfrom ground to the output line Ob as the current I33, due to the factthat the transistor Tr33 turns into an ON state.

Although the present invention has been described in accordance with theembodiments, it will be obvious that various modifications to thepresent invention may be made without changing the gist of theinvention.

1. An ultrasonic transducer driving circuit comprising: a voltage output type circuit configured to control an output voltage and to supply an electrical current to an output line for driving an ultrasonic transducer; and a buffer amplifier along an output line of said voltage output type circuit, the buffer amplifier configured to receive an output voltage of said voltage output type circuit, said buffer amplifier comprising: a first push-pull circuit of comprising a first transistor and a second transistor connected to an output line of the buffer amplifier; and a second push-pull circuit comprising a third transistor and a fourth transistor connected between the output line of said buffer amplifier and a ground, wherein each transistor of said first push-pull circuit and said second push-pull circuit is configured to receive a voltage having a predetermined voltage difference relative to the output voltage of said voltage output type circuit; wherein the predetermined voltage difference is larger for said fourth transistor than for said second transistor, such that said fourth transistor has an ON state based on the output voltage of said voltage output type circuit when the output line of said buffer amplifier is at a positive voltage to allow a current arising from electric charges accumulated in the ultrasonic transducer to flow from the output line of said buffer amplifier to the ground; and the predetermined voltage difference is larger for said third transistor than for said first transistor such that said third transistor has an ON state based on the output voltage of said voltage output type circuit when the output line of said buffer amplifier is at a negative voltage to allow the current arising from the electric charges accumulated in the ultrasonic transducer to flow from the ground to the output line of said buffer amplifier.
 2. The ultrasonic transducer driving circuit according to claim 1, wherein said first transistor and said second transistor are connected between the output line of said buffer amplifier and a power supply.
 3. The ultrasonic transducer driving circuit according to claim 2, wherein said first transistor is connected to a positive supply voltage and said second transistor is connected to a negative supply voltage.
 4. The ultrasonic transducer driving circuit according to claim 1, wherein: said first transistor and said third transistor are configured to receive a voltage larger than the output voltage of said voltage output type circuit; and said second transistor and said fourth transistor are configured to receive a voltage smaller than the output voltage of said voltage output type circuit.
 5. An ultrasonic image display apparatus comprising an ultrasonic transducer driving circuit according to claim
 1. 